Optimum operating conditions for the removal of volatile organic compounds in a compost-packed biofilter

Biofiltration was performed for 101 days in a compost-packed biofilter (I.D. 5.0 cmxheight 62 cm) for the removal of nine volatile organic compounds (benzene, toluene,m-xylene,o-xylene, styrene, chloroform, trichloroethylene, isoprene, and dimethyl sulfide). Removal efficiency of the volatile organic compounds (VOCs) was dependent upon the column temperature, gas flow rate, and incoming concentrations of VOCs. At an empty bed residence time (EBRT) of 3 min and the incoming gas concentration of 66 g m^-3 overall removal and efficiency increased up to 92.1 and 86.4% at 25 °C and 45 °C, respectively. Upon further increase of the incoming gas concentration to 83 g m⁻³, the removal efficiency was 93.7% at 25 °C, but dropped to 73.1% at 45 °C. At incoming gas concentration of 92 g m^-3 and EBRT of 1.5 min, the removal efficiency at 25 °C (91.6%) was comparable to 32 °C (95.5%). However, for 1 min of EBRT removal efficiency was better (86.6%) at 32 °C as compared to at 25 °C (73.6%). The maximum removal rates of VOCs were 3,561, 4,196, and 1,150 g m^-3 h^-1 at 25, 32, and 45 °C, respectively. At an EBRT of 1.5 min and 32 °C the removal efficiency of individual component was highest for toluene (98.9%) andm-xylene (97.6%), and lowest for TCE (86.1%) and chloroform (89.4%). Aromatic compounds (benzene, toluene, and xylene) were removed by 97.1–98.9%. After 101 days of operation profiles of pH and moisture content from the top to the bottom of the column were 7.2–6.3 and 53.8–67.2%, respectively, at 32 °C column, and 67% of the incoming VOCs was removed in the first quarter of the column. After 36 days of operation the cell concentration increased 108-fold from its initial value at 25 °C, and reached a maximum of 1.08x108 cells·(g of dry compost)^-1.